Gamma correction for adjustable  light source

ABSTRACT

The present invention provides a projection apparatus comprising: a light source; a light source control unit for controlling output of the light source; at least one spatial light modulator for modulating illumination light from the light source by a plurality of pixel elements; and an optical system for projecting, to a screen, the illumination light deflected by the spatial light modulator, wherein: the light source control unit modulates output of the illumination light from the light source during a modulation period of the spatial light modulator, and non-linearly controls gray scale of a projected image projected to the screen.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a technology that can be advantageously applied to a projection apparatus or the like having a spatial light modulator.

2. Description of the Related Art

Even though there are significant advances made in recent years on the technologies of implementing electromechanical micro-mirror devices as spatial light modulator, there are still limitations and difficulties when employed to provide high quality images display. Specifically, when the display images are digitally controlled, the image qualities are adversely affected due to the fact that the image is not displayed with sufficient number of gray scales.

Electromechanical micro-mirror devices have drawn considerable interest because of their application as spatial light modulators (SLMs). A spatial light modulator requires an array of a relatively large number of micro-mirror devices. In general, the number of devices required ranges from 60,000 to several million for each SLM. Referring to FIG. 1A for a digital video system 1 disclosed in a relevant U.S. Pat. No. 5,214,420 that includes a display screen 2. A light source 10 is used to generate light energy for ultimate illumination of display screen 2. Light 9 generated is further concentrated and directed toward lens 12 by mirror 11. Lens 12, 13 and 14 form a beam columnator to operative to columnate light 9 into a column of light 8. A spatial light modulator 15 is controlled by a computer through data transmitted over data cable 18 to selectively redirect a portion of the light from path 7 toward lens 5 to display on screen 2. The SLM 15 has a surface 16 that includes an array of switchable reflective elements, e.g., micro-mirror devices 32, such as elements 17, 27, 37, and 47 reflective elements attached to a hinge 30 that shown in FIG. 1B. When element 17 is in one position, a portion of the light from path 7 is redirected along path 6 to lens 5 where it is enlarged or spread along path 4 to impinge the display screen 2 so as to form an illuminated pixel 3. When element 17 is in another position, light is not redirected toward display screen 2 and hence pixel 3 would be dark.

The on-and-off states of micro-mirror control scheme as that implemented in the U.S. Pat. No. 5,214,420 and by most of the conventional display system imposes a limitation on the quality of the display. Specifically, when applying conventional configuration of control circuit has a limitation that the gray scale of conventional system (PWM between ON and OFF states) is limited by the LSB (least significant bit, or the least pulse width). Due to the On-Off states implemented in the conventional systems, there is no way to provide shorter pulse width than LSB. The least brightness, which determines gray scale, is the light reflected during the least pulse width. The limited gray scales lead to degradations of image display.

Specifically, in FIG. 1C an exemplary circuit diagram of a prior art control circuit for a micro-mirror according to U.S. Pat. No. 5,285,407. The control circuit includes memory cell 32. Various transistors are referred to as “M*” where * designates a transistor number and each transistor is an insulated gate field effect transistor. Transistors M5, and M7 are p-channel transistors; transistors, M6, M8, and M9 are n-channel transistors. The capacitances, C1 and C2, represent the capacitive loads presented to memory cell 32. Memory cell 32 includes an access switch transistor M9 and a latch 32 a, which is the basis of the static random access switch memory (SRAM) design. All access transistors M9 in a row receive a DATA signal from a different bit-line 31 a. The particular memory cell 32 to be written is accessed by turning on the appropriate row select transistor M9, using the ROW signal functioning as a wordline. Latch 32 a is formed from two cross-coupled inverters, M5/M6 and M7/M8, which permit two stable states. state 1 is Node A high and Node B low and state 2 is Node A low and Node B high.

The dual states switching as illustrated by the control circuit controls the micro-mirrors to position either at an ON of an OFF angular orientation as that shown in FIG. 1A. The brightness, i.e., the gray scales of display for a digitally control image system is determined by the length of time the micro-mirror stays at an ON position. The length of time a micro-mirror is controlled at an ON position is in turned controlled by a multiple bit word. For simplicity of illustration, FIG. 1D shows the “binary time intervals” when control by a four-bit word. As that shown in FIG. 1D, the time durations have relative values of 1, 2, 4, 8 that in turn define the relative brightness for each of the four bits where 1 is for the least significant bit and 8 is for the most significant bit. According to the control mechanism as shown, the minimum controllable differences between gray scales for showing different brightness is a brightness represented by a “least significant bit” that maintaining the micro-mirror at an ON position.

In a simple example, and assuming n bits of gray scales, the frame time is divided into 2″−1 equal time slices. For a 16.7 milliseconds frame period and n-bit intensity values, the time slice is 16.7/(2″−1) milliseconds

Having established these times, for each pixel of each frame, pixel intensities are quantized, such that black is 0 time slices, the intensity level represented by the LSB is 1 time slice, and maximum brightness is 2″−1 time slices. Each pixel's quantized intensity determines its on-time during a frame period. Thus, during a frame period, each pixel with a quantized value of more than 0 is on for the number of time slices that correspond to its intensity. The viewer's eye integrates the pixel brightness so that the image appears the same as if it were generated with analog levels of light.

For addressing deformable mirror devices, PWM calls for the data to be formatted into “bit-planes”, each bit-plane corresponding to a bit weight of the intensity value. Thus, if each pixel's intensity is represented by an n-bit value, each frame of data has n bit-planes. Each bit-plane has a 0 or 1 value for each display element. In the PWM example described in the preceding paragraphs, during a frame, each bit-plane is separately loaded and the display elements are addressed according to their associated bit-plane values. For example, the bit-plane representing the LSBs of each pixel is displayed for 1 time slice.

Projection apparatuses such as described above generally use a light source such as a high-pressure mercury lamp, a xenon lamp, or the like. However, these types of light sources are poor in performing high-speed switching between ON and OFF.

Also, there is an increasing demand that projection apparatuses should display (project) images at a higher level of gray scale (gradation). Accordingly, a spatial light modulator has to be controlled to permit a projection apparatus to project images at a higher level of gray scale. However, if the improvement of the gray scale performance is to be achieved only through the control of the spatial light modulator, the improvement would be only to a limited level.

Due to a course of the development of the image displaying technology in the past, a so-called γ correction is performed on the side of cameras when imaging is carried out in order to correspond to the emission characteristics of CRT display devices, which are representative display devices for the television broadcasting.

This means that, in the CRT devices of televisions, the relationship between an applied signal voltage E and an emission output L can be represented by L=E^(γ) in other words, the relationship is non-linear. Also, this γ correction is performed on the transmission side (where image data is generated) in order to suppress the cost of television receivers, image reproduction devices, etc.

By contrast, the display characteristic of projection apparatuses using micro-mirror devices as described above is linear unlike the CRT devices. Accordingly, it is necessary to perform a reverse correction on the broadcasted image signals in order to cancel the γ correction performed on the transmission side.

An example of the γ correction performed on the reception side is a γ correction in which a prescribed mathematical operation is performed on the input data itself. However, the processing of this mathematical operation for the γ correction is complicated because of using the logarithm function. Also, an operation circuit that is of a larger scale is required so as to increase production costs of projection apparatuses.

It is also possible to adapt a conversion technology using a lookup table or the like thereby avoiding the use of mathematical operations. However, in order to attain an acceptable operation accuracy (conversion accuracy), the gray scale accuracy of input data has to be increased (in other words, the number of bits has to be increased) before the conversion, which forces the lookup table or the like to occupy a greater volume of memory so as to increase production costs of projection apparatuses.

-   Patent Document 1: U.S. Pat. No. 5,214,420 -   Patent Document 2: U.S. Pat. No. 5,285,407

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a technology that realizes various and high performance display gray scale without being limited by the display gray scale performance of a spatial light modulator in a projection apparatus having a spatial light modulator.

It is another object of the present invention to realize a technology that permits a gamma correction in a projection apparatus having a spatial light modulator without making the configuration complicated or increasing costs.

A first aspect of the present invention provides a projection apparatus, comprising:

a light source;

a light source control unit for controlling output of the light source;

at least one spatial light modulator for modulating illumination light from the light source by a plurality of pixel elements; and

an optical system for projecting, to a screen, the illumination light deflected by the spatial light modulator, wherein:

the light source control unit modulates output of the illumination light from the light source during a modulation period of the spatial light modulator, and non-linearly controls gray scale of a projected image projected to the screen.

A second aspect of the present invention provides the projection apparatus according to the first aspect, wherein:

the light source control unit modulates output of the illumination light by making an intensity of the illumination light variable.

A third aspect of the present invention provides the projection apparatus according to the first aspect, wherein:

the light source control unit modulates output of the illumination light by making an emission interval cycle of pulse emission of the light source variable.

A fourth aspect of the present invention provides the projection apparatus according to the first aspect, wherein:

the light source control unit modulates output of the illumination light by making an emission interval cycle of pulse emission of the light source constant and by making an emission pulse time variable.

A fifth aspect of the present invention provides the projection apparatus according to the first aspect, wherein:

the light source control unit modulates output of the illumination light by making an emission interval cycle and an emission pulse time of pulse emission of the light source variable.

A sixth aspect of the present invention provides the projection apparatus according to the first aspect, wherein:

the light source control unit modulates output of the illumination light by making at least one of an emission interval cycle, an emission pulse time, and an emission pulse intensity of pulse emission of the light source variable.

A seventh aspect of the present invention provides the projection apparatus according to the first aspect, wherein:

the light source control unit modulates output of the illumination light by input image data.

A eighth aspect of the present invention provides the projection apparatus according to the first aspect, wherein:

the light source control unit increases maximum brightness of the light source by making an emission interval cycle of the pulse emission variable within a particular time of one frame when output of the illumination light is modulated by making an emission interval cycle of pulse emission of the light source variable.

A ninth aspect of the present invention provides the projection apparatus according to the first aspect, wherein:

the spatial light modulator comprises a micromirror device in which a plurality of mirror elements for deflecting light from the light source are arranged.

A tenth aspect of the present invention provides the projection apparatus according to the first aspect, wherein:

the light source is a light emitting diode (LED) or a laser device.

An eleventh aspect of the present invention provides a projection apparatus, comprising:

at least one light source provided for each of colors of illumination light;

a light source control unit for controlling output of the light source;

at least one spatial light modulator for modulating the illumination light from the light source by a plurality of pixel elements; and

an optical system for projecting, to a screen, the illumination light modulated by the spatial light modulator, wherein:

the light source control unit modulates a projected image by changing an emission energy of cyclic pulse emission for each color of the illumination light emitted from the light source.

A twelfth aspect of the present invention provides the projection apparatus according to the eleventh aspect, wherein:

the light source control unit changes emission pulse width of the cyclic pulse emission for each color of the illumination light emitted from the light source.

A thirteenth aspect of the present invention provides the projection apparatus according to the eleventh aspect, wherein:

the light source control unit changes an emission pulse cycle of the cyclic pulse emission for each color of the illumination light emitted from the light source.

A fourteenth aspect of the present invention provides the projection apparatus according to the eleventh aspect, wherein:

the light source control unit changes an emission pulse intensity of the cyclic pulse emission for each color of the illumination light emitted from the light source.

A fifteenth aspect of the present invention provides the projection apparatus according to the eleventh aspect, wherein:

the light source control unit changes an emission interval cycle and emission pulse width of the cyclic pulse emission for each color of the illumination light emitted from the light source.

A sixteenth aspect of the present invention provides the projection apparatus according to the eleventh aspect, wherein:

the light source control unit changes an emission interval cycle and an emission pulse intensity of the cyclic pulse emission for each color of the illumination light emitted from the light source.

A seventeenth aspect of the present invention provides the projection apparatus according to the eleventh aspect, wherein:

the light source control unit changes emission pulse width and an emission pulse intensity of the cyclic pulse emission for each color of the illumination light emitted from the light source.

A eighteenth aspect of the present invention provides the projection apparatus according to the eleventh aspect, wherein:

the spatial light modulator comprises a micromirror device in which a plurality of mirror elements for deflecting light from the light source are arranged.

A nineteenth aspect of the present invention provides the projection apparatus according to the eleventh aspect, wherein:

the light source is a light emitting diode (LED) or a laser device.

A twentieth aspect of the present invention provides the projection apparatus according to the eleventh aspect, wherein:

the light source control unit demodulates output of the illumination light by input image data.

A twenty-first aspect of the present invention provides a projection apparatus, comprising:

at least one light source provided for each of colors of illumination light;

a light source control unit for controlling output of the light source;

at least one micromirror device in which a plurality of mirror elements for deflecting the illumination light from the light source are arranged;

a micromirror device control unit for controlling the micromirror device; and

a projection optical system for projecting, to a screen, the deflected illumination light from the micromirror device, wherein:

the light source control unit performs a modulation control of an accumulated maximum light intensity in a display period of one frame corresponding to the light source of each color of the illumination light.

A twenty-second aspect of the present invention provides the projection apparatus according to the twentieth-first aspect, wherein:

the micromirror device control unit causes the mirror element corresponding to pixel data of maximum brightness in the frame data for each color to be in a state of continuously leading the illumination light to the projection optical system during a display term of the one frame; and

the light source control unit performs a modulation control so that a desired output light intensity corresponding to the pixel data of the maximum brightness is obtained.

A twenty-third aspect of the present invention provides the projection apparatus according to the twentieth-first aspect, wherein:

the light source is a light emitting diode (LED) or a laser device.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described in detail below with reference to the following figures.

FIG. 1A is a conceptual diagram showing the configuration of a projection apparatus according to a conventional technique;

FIG. 1B is a conceptual diagram showing the configuration of a mirror element of the projection apparatus according to a conventional technique;

FIG. 1C is a conceptual diagram showing the configuration of the drive circuit of a mirror element of the projection apparatus according to a conventional technique;

FIG. 1D is a conceptual diagram showing the format of image data used in the projection apparatus according to a conventional technique;

FIG. 1E is an illustrative diagram for describing etendue by exemplifying the case of using a discharge lamp light source and projecting an image by way of an optical device;

FIG. 2 is a diagram showing the relationship among the numerical aperture NA1 of an illumination light path, the numerical aperture NA2 of a projection light path and the tilt angle a of a mirror;

FIG. 3A is a plan cross-sectional view exemplifying a configuration example of a mirror device according to a preferred embodiment 1-1;

FIG. 3B is a cross-sectional view of a part along line B-B′ in a configuration example of a mirror element in the mirror device shown in FIG. 3A according to the preferred embodiment 1-1;

FIG. 3C is a cross-sectional view of a part along line A-A′ in a configuration example of the mirror element in the mirror device shown in FIG. 3A according to a preferred embedment 1-1;

FIG. 4 shows another configuration example of an electrode;

FIG. 5A is a side view diagram showing an example of a deflection state when the mirror is ON;

FIG. 5B is a side view diagram showing an example of a deflection state when the mirror is OFF;

FIG. 5C is another side view diagram showing an example of the deflection state when the mirror is OFF;

FIG. 6 is a conceptual diagram showing the configuration of a projection apparatus according to a preferred embodiment of the present invention;

FIG. 7 is a conceptual diagram showing the configuration of a single-panel projection apparatus according to another preferred embodiment of the present invention;

FIG. 8A is a block diagram showing the configuration of a control unit provided to a single-panel projection apparatus according to a preferred embodiment of the present invention;

FIG. 8B is a block diagram showing the configuration of a the control unit of a multi-panel projection apparatus according to a preferred embodiment of the present invention;

FIG. 9 is a conceptual diagram exemplifying the configuration of the light source drive circuit of a projection apparatus according to a preferred embodiment of the present invention;

FIG. 10 is a chart showing the relationship between the applied current and the intensity of emission of the light source drive circuit according to the embodiment of the present invention;

FIG. 11 is a conceptual diagram exemplifying the layout of the internal configuration of a spatial light modulator according to the embodiment of the present invention;

FIG. 12 is a cross-sectional diagram of an individual pixel unit constituting a spatial light modulator according to the preferred embodiment of the present invention;

FIG. 13 is a conceptual diagram exemplifying the configuration of individual pixel unit constituting a spatial light modulator according to the embodiment of the present invention;

FIG. 14 is a chart describing the principle of a γ correction of video image data

FIG. 15 is a chart showing the principle of a γ correction by means of a control of the emission intensity of a light source performed in a projection apparatus according to the embodiment of the present invention;

FIG. 16 is a chart describing an example of conversion from binary data to non-binary data performed in a projection apparatus according to the embodiment of the present invention;

FIG. 17 is a chart describing an example of conversion from binary data to non-binary data performed in a projection apparatus according to the embodiment of the present invention;

FIG. 18 is a chart describing an example of conversion from binary data to non-binary data performed in a projection apparatus according to the embodiment of the present invention;

FIG. 19 is a chart describing an example of conversion from binary data to non-binary data performed in a projection apparatus according to the embodiment of the present invention;

FIG. 20 is a chart showing a γ correction of a brightness input in eight-bit non-binary data, by exemplifying the implementation in four stages, performed in a projection apparatus according to the embodiment of the present invention;

FIG. 21 is a chart showing a γ correction of a brightness input in eight-bit non-binary data, by showing a modification of the implementation in four stages, performed in a projection apparatus according to the embodiment of the present invention;

FIG. 22 is a chart exemplifying a γ correction by means of an intermittent pulse emission performed in a projection apparatus according to the embodiment of the present invention;

FIG. 23A is a chart exemplifying a γ correction by means of an intermittent pulse emission, thereby increasing a correction effect on the lower brightness side, performed in a projection apparatus according to the embodiment of the present invention;

FIG. 23B is a chart exemplifying the γ correction curve performing a γ correction by means of a light source pulse pattern exemplified in FIG. 23A, thereby increasing a correction effect on the lower brightness side;

FIG. 24A is a chart exemplifying the case of performing a γ correction considering the visual characteristic of human being by means of an intermittent pulse emission in a projection apparatus according to the embodiment of the present invention;

FIG. 24B is a chart exemplifying the case of performing a γ correction considering the visual characteristic of human being by means of the light source pulse pattern exemplified in FIG. 24A;

FIG. 25 is a chart exemplifying the case of performing a gray scale control by keeping a mirror in a constant ON state and controlling the intensity of emission of a light source, which is performed in a multi-panel projection apparatus according to the embodiment of the present invention;

FIG. 26 is a chart exemplifying the case of performing a gray scale control by keeping a mirror in a constant ON state and controlling the pulse emission of a light source, which is performed in a multi-panel projection apparatus according to the embodiment of the present invention;

FIG. 27 is a chart exemplifying the case of performing a gray scale control by keeping a mirror in a constant ON state and controlling the intensity of emission of a light source, which is performed in a single-panel projection apparatus according to the embodiment of the present invention;

FIG. 28 is a chart exemplifying the case of performing a gray scale control by keeping a mirror in a constant ON state and controlling the pulse emission of a light source, which is performed in a single-panel projection apparatus according to the embodiment of the present invention;

FIG. 29 is a diagram describing the principle of increasing the range of a gray scale control by a combination between the ON/OFF control of a mirror and the emission intensity control of a light source, which is performed in a projection apparatus according to the embodiment of the present invention; and

FIG. 30 is a chart exemplifying the case of preventing a color break by a combination between the ON/OFF control of a mirror and the oscillation control of the mirror performed in a projection apparatus according to the embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will be explained by referring to <<Disclosure Contents>>provided below.

<<Disclosure Content 1>> Preferred Embodiment 1-1

A preferred embodiment 1-1 of the present invention relates to a mirror device configured to arranging a plurality of deflectable mirrors in array and further specifically to a method for regulating the deflection angle of a mirror.

FIG. 1E is an illustrative diagram for showing etendue by exemplifying the case of using a discharge lamp light source and projecting an image by way of an optical device.

[Outline of the Device]

The first is a description of a mirror device.

Projection apparatuses each generally using a spatial light modulator, such as a transmissive liquid crystal, a reflective liquid crystal, a mirror array and the like, are widely known.

A spatial light modulator is formed as a two-dimensional array arranging from tens of thousands to millions of miniature modulation elements, with the individual elements enlarged and displayed, as the individual pixels corresponding to an image to be displayed, onto a screen by way of a projection lens.

The spatial light modulators generally used for projection apparatuses primarily include two types, i.e., a liquid crystal device for modulating the polarizing direction of incident light by sealing a liquid crystal between transparent substrates and providing them with a potential, and a mirror device deflecting miniature micro electro mechanical systems (MEMS) mirrors with electrostatic force and controlling the reflecting direction of illumination light.

One embodiment of the above described mirror device is disclosed in U.S. Pat. No. 4,229,732, in which a drive circuit using MOSFET and deflectable metallic mirrors are formed on a semiconductor wafer substrate. The mirror allows to be deformed by electrostatic force supplied from the drive circuit and is capable of changing the reflecting direction of the incident light.

Meanwhile, U.S. Pat. No. 4,662,746 has disclosed an embodiment in which one or two elastic hinges retain a mirror. If the mirror is retained by one elastic hinge, the elastic hinge functions as bending spring. If the mirror is retained by two elastic hinges, they function as torsion springs to incline the mirror and thereby the reflecting direction of the incident light is deflected.

As described above, the on-and-off states of micromirror control scheme as that implemented in the U.S. Pat. No. 5,214,420 and by most of the conventional display system imposes a limitation on the quality of the display. Specifically, when applying conventional configuration of control circuit has a limitation that the gray scale of conventional system (PWM between ON and OFF states) is limited by the LSB (least significant bit, or the least pulse width). Due to the On-Off states implemented in the conventional systems, there is no way to provide shorter pulse width than LSB. The least brightness, which determines gray scale, is the light reflected during the least pulse width. The limited gray scales lead to degradations of image display.

Specifically, in FIG. 1C an exemplary circuit diagram of a prior art control circuit for a micromirror according to U.S. Pat. No. 5,285,407. The control circuit includes memory cell 32. Various transistors are referred to as “M*” where * designates a transistor number and each transistor is an insulated gate field effect transistor. Transistors M5, and M7 are p-channel transistors; transistors, M6, M8, and M9 are n-channel transistors. The capacitances, C1 and C2, represent the capacitive loads presented to memory cell 32. Memory cell 32 includes an access switch transistor M9 and a latch 32 a, which is the basis of the static random access switch memory (SRAM) design. All access transistors M9 in a row receive a DATA signal from a different bit-line 31 a. The particular memory cell 32 to be written is accessed by turning on the appropriate row select transistor M9, using the ROW signal functioning as a wordline. Latch 32 a is formed from two cross-coupled inverters, M5/M6 and M7/M8, which permit two stable states. state 1 is Node A high and Node B low and state 2 is Node A low and Node B high.

The mirror driven by a drive electrode abuts on a landing electrode structured differently from the drive electrode, and thereby a prescribed tilt angle is maintained. A “landing chip”, which possesses a spring property, is formed on the contact part abutting on the landing electrode so that an operation of the mirror deflecting to the reverse direction upon changing over the control is assisted. The part forming the landing chip and the landing electrode are maintained at the same potential so that the contact will not cause a shorting or the like.

[Outline of PWM Control]

Next is an outline of a pulse-width modulation (PWM) control.

As described above, the dual states switching as illustrated by the control circuit controls the micromirrors to position either at an ON of an OFF angular orientation as that shown in FIG. 1A. The brightness, i.e., the gray scales of display for a digitally control image system is determined by the length of time the micromirror stays at an ON position. The length of time a micromirror is controlled at an ON position is in turned controlled by a multiple bit word. For simplicity of illustration, FIG. 1D shows the “binary time intervals” when control by a four-bit word. As that shown in FIG. 1D, the time durations have relative values of 1, 2, 4, 8 that in turn define the relative brightness for each of the four bits where 1 is for the least significant bit and 8 is for the most significant bit. According to the control mechanism as shown, the minimum controllable differences between gray scales for showing different brightness is a brightness represented by a “least significant bit” that maintaining the micromirror at an ON position.

In a simple example, and assuming n bits of gray scales, the frame time is divided into (2^(n)−1) equal time slices. For a 16.7 milliseconds frame period and n-bit intensity values, the time slice is 16.7/(2^(n)−1) milliseconds

Having established these times, for each pixel of each frame, pixel intensities are quantized, such that black is 0 time slices, the intensity level represented by the LSB is 1 time slice, and maximum brightness is 15 time slices (in the case of n=4). Each pixel's quantized intensity determines its on-time during a frame period. Thus, during a frame period, each pixel with a quantized value of more than 0 is on for the number of time slices that correspond to its intensity. The viewer's eye integrates the pixel brightness so that the image appears the same as if it were generated with analog levels of light.

For addressing deformable mirror devices, PWM calls for the data to be formatted into “bit-planes”, each bit-plane corresponding to a bit weight of the intensity value. Thus, if each pixel s intensity is represented by an n-bit value, each frame of data has n bit-planes. Each bit-plane has a 0 or 1 value for each display element. In the PWM example described in the preceding paragraphs, during a frame, each bit-plane is separately loaded and the display elements are addressed according to their associated bit-plane values. For example, the bit-plane representing the LSBs of each pixel is displayed for 1 time slice.

[Outlines of Mirror Size and Resolution]

Next is an outline description of the size of a mirror and the resolution.

The size of a mirror for constituting such a mirror device is between 4 μm and 20 μm for each side, and the mirrors are placed on a semiconductor wafer substrate in such a manner as to minimize the gap between adjacent mirrors so that useless reflection light from the gap does not degrade the contrast of a demodulated image. One mirror device is constituted by forming on a substrate an appropriate number of mirror elements, as image display elements, comprising these mirrors. Here, the appropriate number as image display elements are the numbers, for example, in compliance to the resolution of a display specified by the Video Electronics Standards Association (VESA) and to the television forecasting standard. Here, in the case of configuring a mirror device comprising the number of mirror elements, which is compliant to the WXGA (with the resolution of 1280×768) specified by the VESA and in which the size of each mirror is 10 μm, a sufficiently miniature mirror device is configured, with about 0.61 inches of the diagonal length of the display area.

[Outline of Projection Apparatus]

Next is an outline description of the configuration of a projection apparatus.

The projection apparatuses using deflection-type (“deflectable”) light modulators are primarily categorized into two types, i.e., a single-panel projection apparatus comprising a single spatial light modulator, changing spatially the frequency of a projection light and displaying an image in colors, and a multi-panel projection apparatus comprising a plurality of spatial light modulators, modulating an illumination light with different frequencies constantly by means of the individual spatial light modulators and displaying an image in colors by synthesizing these modulated lights.

The single-panel projection apparatus is constituted as described above by referring to FIG. 1A.

[Outline of the Introduction of Laser Light Source]

Next is an outline description of the introduction of a laser light source.

In the projection apparatus comprising a reflective spatial light modulator represented by the above described mirror, there is a close relationship among the numerical aperture (NA) NA1 of an illumination light path, the numerical aperture NA2 of a projection light path and the tilt angle a of a mirror. FIG. 2 shows the relationship among them.

Let it be assumed that the tilt angle a of a mirror 1011 as 12 degrees. When a modulated light reflected by the mirror 1011 and incident to the pupil of the projection light path is set at the perpendicular direction of a device substrate 1012, the illumination light is incident from a direction inclined by 2α, that is, 24 degrees, relative to the perpendicular of the device substrate 1012. For the light beam reflected by the mirror to be most efficiently incident to the pupil of the projection lens, the numerical aperture of the projection light path is desirably equal to the numerical aperture of the illumination light path. If the numerical aperture of the projection light path is smaller than that of the illumination light path, the illumination light cannot be sufficiently imported into the projection light path, while if the numerical aperture of the projection light path is larger that that of the illumination light path, the illumination light can be entirely imported; the projection lens becomes unnecessarily large, bringing about inconvenience in terms of configuring the projection apparatus. Further in this event, the light fluxes of the illumination light and projection light need to be basically placed apart from each other because the optical members of the illumination system and those of the projection system need to be physically placed respectively. From the above considerations, when a spatial light modulator with the tilt angle of a mirror being 12 degrees is used, the numerical aperture (NA) NA1 of the illumination light path and the numerical aperture NA2 of the projection light path are preferred to be set as follows:

NA1=NA2=sin α=sin 12°

Letting the F number of the illumination light path be F1 and the F number of the projection light path be F2, then the numerical aperture can be converted into an F number as follows:

F1=F2=1/(2*NA)=)1/(2*sin 12°)=2.4

In order to maximize the importation of illumination light emitted from a light source possessing non-directivity in the emission direction of light, such as a high-pressure mercury lamp and xenon lamp, which are generally used for a projection apparatus, there is a requirement for maximizing the importing angle of light on the illumination light path side. Considering that the numerical aperture of the illumination light path is determined by the specification of the tilt angle of a mirror to be used, it is clear that the tilt angle of the mirror needs to be large for increasing the numerical aperture of the illumination light path.

However, there is a problem that the increasing of the tilt angle of mirror requires a higher drive voltage for driving the mirror.

Because greater tilt angle of the mirror requires a physical space for tilting the mirror, a greater distance needs to be secured between the mirror and an electrode for driving the mirror. The electrostatic force F generated between the mirror and the electrode is given by the following expression:

F=(ε*S*V ²)/(2*d ²),

where “S” is the area size of the electrode, “V” is a voltage, “d” is the distance between the electrode and mirror and “ε” is the permittivity of vacuum.

The expression makes it comprehensible that the drive force is decreased in proportion to the second power of the distance d between the electrode and mirror. It is conceivable to increase the drive voltage for compensating the decrease in the drive force associated with the increase in the distance; conventionally, however, the drive voltage is about 3 to 15 volts in the drive circuit by means of a CMOS process used for driving a mirror and therefore a relatively special process such as a DMOS process is required if a drive voltage in excess of about 15 volts is needed. That is not preferable in view of the purchase of a mirror device and the cost reduction.

Further, as for a cost reduction of a mirror device, it is desirable to obtain as many mirror devices as possible from a single semiconductor wafer substrate in view of the improvement of productivity. That is, a miniaturization of the size of mirror elements reduces the size of the mirror device per se. It is clear that the area size of an electrode is reduced in association with the miniaturization of the mirror, which also leads to less driving power in accordance with the above expression.

Furthermore, in contrast to the requirement for miniaturizing a mirror device, there is a problem in which the larger a mirror device, the brighter is it possible to illuminate as long as a conventional lamp is used because a conventional lamp with a non-directivity in its emission allows the usage efficiency of light to be substantially reduced. This is attributable to a relationship commonly called etendue.

As shown in FIG. 1E above, where “y” is the size of a light source 4150, “u” is the importing angle of light on the light source side of the illumination lens 4106, “y′” is the size of the image of a light source, and “u′” is the converging angle on the image side (device 4107), the relationship among these in a case when the projected image is to be projected via the device 4107 and the projection lens is represented by the following expression:

y*u=y′*u′

That is, the smaller the device on which a light source is intended to be imaged, the smaller the importing angle on the light source side becomes. This is why it is advantageous to use a laser light source, of which the emission light possesses strong directivity, for miniaturizing a mirror device. [Outline of Resolution Limit]

Next is an outline description of a resolution limit.

An examination of the limit value of the aperture ratio of a projection lens used for a projection apparatus, which displays the display surface of a spatial light modulator in enlargement, in view of the resolution of an image to be projected, leads to the following.

Where “Rp” is the pixel size of the spatial light modulator, “NA” is the aperture ratio of a projection lens, “F” is an F number and “A” is the wavelength of light, the limitative “Rp” with which any adjacent pixels on the projection surface are separately observed is given by the following expression:

Rp=0.61*λ/NA=1.22*λ*F

The table below shows the F value of a projection lens and deflection angle of a mirror when the size of adjacent mirror elements is shortened by miniaturizing the mirror elements, with the wavelength of light beam designated at λ=650 nm that is the worst condition within the range of visible light. Meanwhile, the F value of a projection lens with the wavelength designated at 700 nm is about 7% smaller than the case of calculating the F value for the wavelength of 650 nm.

Pixel size of mirror device F number of Deflection angle of [μm] projection lens mirror [degrees] 4 5.04 5.69 5 6.30 4.55 6 7.56 3.79 7 8.82 3.24 8 10.08 2.84 9 11.34 2.52 10 12.61 2.27 11 13.87 2.06

Therefore, if the problem related to the above described etendue is avoided by using a laser light for the light source, the F numbers of lenses for the illumination system and projection system can be increased to the values shown in the table, making it possible to decrease the deflection angle of the mirror element and thereby a miniature mirror device with a low drive voltage can be configured.

[Outline of Oscillation Control]

Next is an outline description of an oscillation control.

As another method for reducing a drive voltage, other than the method for minimizing the tilt angle of a mirror, there is a technique disclosed in US Patent Application 20050190429. In this disclosure, a mirror is put to a free oscillation in the inherent oscillation frequency, and thereby the intensity of light that is about 25% to 37% of the emission light intensity when a mirror is controlled under a constant ON can be obtained during the oscillation period of the mirror.

According to such a control, there is no particular need to drive the mirror in high speed, making it possible to obtain a high level of gray scale with a low spring constant of a spring member supporting the mirror, and therefore enabling a reduction in the drive voltage. Furthermore, a combination with the method of decreasing the drive voltage by decreasing the deflection angle of a mirror as described above brings forth a greater deal of effect.

As described above, the use of a laser light source makes it possible to decrease the deflection angle of a mirror and also miniaturize the mirror device without ushering in a degradation of brightness, and further, the use of the above described oscillation control enables a higher level of gray scale without causing an increase in the drive voltage.

There is, however, the problem of degrading the efficiency of space usage of an electrode if an electrode for driving a mirror and a stopper for determining the deflection angle of the mirror are individually configured as in the conventional method.

U.S. Pat. No. 5,583,688, US Patent 20060152690, U.S. Pat. No 6,198,180, and U.S. Pat. No. 6,992,810 disclose configurations for determining a deflection angle of a mirror in a conventional mirror device. However, in any of the above disclosed configurations, it is difficult to increase the size of address electrodes. In consideration of the problems noted above, the preferred embodiment 1-1 of the present invention is accordingly configured to integrally form an electrode used for driving a mirror element and a stopper used for determining the deflection angle of a mirror, in a mirror device.

The following is a description, in detail, of a mirror device according to the present embodiment.

FIG. 3A is a horizontal cross-sectional diagram exemplifying the configuration of the mirror element of a mirror device according to the preferred embodiment 1-1.

FIG. 3B is a side cross-sectional diagram exemplifying the configuration of the mirror element of the mirror device according to the preferred embodiment 1-1. FIG. 3C is another side cross-sectional diagram showing the configuration of the mirror element of the mirror device according to the preferred embodiment of 1-1.

In the mirror element shown in FIGS. 3A, 3B, 3C, a mirror 1101 made of a high reflectance material such as aluminum and gold is supported by an elastic hinge 1102 made of a silicon material, a metallic material and the like, and is placed on a substrate member 1103. Here, the silicon material comprehends poly-silicon, single crystal silicon and amorphous silicon, while the metallic material comprehends aluminum, titanium and an alloy of some of these metallic materials, or a composite material of them. The mirror 1101 has the form of approximate square, with the length of one side, for example, between 4 μm and 11 μm. The size of adjacent mirrors is between, for example, 4 μm and 11 μm. The deflection axis 1111 of the mirror 1101 is on the diagonal line. The lower end of the elastic hinge 1102 is connected to the substrate member 1103 that includes a circuit for driving the mirror 1101. The upper end of the elastic hinge 1102 is connected to the bottom surface of the mirror 1101. For example, an electrode for securing an electrical continuity and an intermediate member for improving the strength of a member and improving the strength of connection may be placed between the elastic hinge and substrate member 1103, or between the elastic hinge 1102 and mirror 1101.

In FIGS. 3A through 3C, electrodes 1104 (i.e., 1104 a and 1104 b) used for driving the mirror 1101 are placed on the top surface of the substrate member 1103 so as to be opposite to the bottom surface of the mirror 1101. The form of the electrode 1104 may be symmetrical or asymmetrical about the deflection axis 1111. The electrode 1104 is made of aluminum or tungsten. The present embodiment is configured such that the electrode 1104 fills the function of a stopper for determining the deflection angle of the mirror. The deflection angle of the mirror is the angle determined by the aperture ratio of a projection lens that satisfies a theoretical resolution determined by the size of adjacent mirrors on the basis of the expression described above:

Rp=0.61*λ/NA=1.22*λ*F

Alternatively, it may be changed to an angle larger than the determined angle. As an example, the deflection angle of mirror is between 10 degrees and 14 degrees relative to the horizontal state of the mirror 1101 or between 2 degrees and 10 degrees relative to the horizontal state of the mirror 1101. The configuring of the electrode 1104 also functioning as stopper makes it possible to maximize an electrode layout space than the conventional case of placing the electrode and stopper individually, when the mirror element is miniaturized.

The form of the electrode is configured, as shown in FIGS. 3A through 3C, to be a trapezoid constituted by the top side and bottom side, which are approximately parallel to the deflection axis 1111 and sloped sides approximately parallel to the contour line of the mirror 1101 of the mirror device in which the deflection axis of the mirror 1101 is matched with the diagonal line thereof. The electrode and stopper are not individually formed as the conventional method, and therefore such a form is available.

A difference in potentials needs to be generated between the mirror and electrode for driving the mirror by electrostatic force. The present embodiment using the electrode also as stopper is configured to provide the surface of the electrode or/and the rear surface of the mirror with an insulation layer(s) in order to prevent an electrical shorting at the mirror contacting with the electrode. Further, in the case of providing the surface of the electrode with an insulation layer, the configuration may also be such that the insulation layer is provided to only a part including the contact part with the mirror. FIGS. 3A through 3C exemplify the case of providing the surface of the electrode 1104 (i.e., 1104 a and 1104 b) with an insulation layer 1105 (i.e., 1105 a and 1105 b). The insulation layer is made of oxidized compound, azotized compound, silicon or silicon compound, e.g., SiC, SiO₂, Al₂O₃, and Si. The material and thickness of the insulation layer is determined so that the dielectric strength voltage is maintained at no less than the voltage required to drive the mirror, most preferably no less than 5 volts. For example, the dielectric strength voltage may be configured to be two times the drive voltage of the mirror or higher, 3 volts or higher or 10 volts or higher.

Next is a description of one example related to the size and form of an electrode.

Referring to FIG. 4, where “L1” is the distance between the deflection axis and the edge of the electrode on a side closer to the deflection axis of the mirror 1101, “L2” is the distance between the deflection axis and the edge of the electrode on a side far from the deflection axis of the mirror 1101, and “d1” and “d2” are the distance between the mirror bottom surface and electrode at the respective edges. Now for a description, “P1” is a representative point at the electrode edge on the side closer to the deflection axis of the mirror and “P2” is a representative point at the electrode edge on the side far from the deflection axis of the mirror.

The example shown in FIG. 4 is the case in which the electrode is formed so as to constitute: d1<d2. In this configuration, the stopper determining the tilt angle of the mirror 1101 is preferred to be placed at the point P2 in consideration of a production variance of the electrode height that influences the deflection angle of the mirror. The present embodiment is accordingly configured to satisfy the relationship of:

d1>(L1*d2)/L2

This configuration provides a good usage efficiency of the space under the mirror and maintains a stable deflection angle of the mirror.

Further, in the case of configuring the electrode to constitute d1=d2, the point on the electrode determining the deflection angle of the mirror is P2 and the configuration is determined to satisfy the following expression:

cot θ=d2/L2

Next is an outline description of the circuit comprisal of the mirror device according to the present embodiment.

The circuit comprisal of the mirror device according to the present embodiment is exemplified in FIGS. 11 and 13, both of which are described later, and therefore the description is not provided here.

Such configuration and operation cause the deflection states of the mirror to change on the basis of the voltage applied to the electrode in each mirror element of a mirror array and thereby the light incident to the mirror 1212 is deflected to the specific direction as shown in FIGS. 5A through 5C as an example.

Next is an outline description of the natural oscillation frequency of the oscillation system of a mirror device according to the present embodiment.

The fact that a drive voltage can be lowered by obtaining a fine gray scale by means of a free oscillation of a mirror is already described above. Now, if an LSB light intensity by way of a common PWM drive is intended to be obtained by an oscillation, the natural oscillation cycle of an oscillation system that includes an elastic hinge is designated as follows:

The natural oscillation cycle T of an oscillation system =2*π*√(I/K)=LSB time/X [%];

where:

I: the rotation moment of an oscillation system,

K: the spring constant of an elastic hinge,

LSB time: the LSB cycle at displaying n bits, and

X [%]: the ratio of the light intensity obtained by one oscillation cycle to the Full-ON light intensity of the same cycle

Note that:

“I” is determined by the weight of a mirror and the distance between the center of gravity and the center of rotation;

“K” is determined from the thickness, width, length and cross-sectional shape of an elastic hinge;

“LSB time” is determined from one frame time, or one frame time and the number of reproduction bits in the case of a single-panel projection method;

“X” is determined as the above description, particularly from the F number of a projection lens and the intensity distribution of an illumination light.

As an example, when a single-panel color sequential method is employed, the ratio of emission intensity by one oscillation is assumed to be 32% and the minimum emission intensity in a 10-bit grayscale is desired to be obtained by an oscillation, then “I” and “K” are designed so as to have a natural oscillation cycle as follows:

T=1/(60*3*2¹⁰*0.32)=17.0 μsec.

In contrast, when a conventional PWM control is employed to make the changeover transition time t_(M) of a mirror approximately equal to the natural oscillation frequency of the oscillation system of the mirror and also the LSB is regulated so that a shortage of the light intensity in the interim can be sufficiently ignored, the gray scale reproducible with the above described hinge is about 8-bit even if the LSB is set at five times the changeover transition time t_(M). That is, it is comprehensible that a 10-bit grayscale can be reproduced by using the elastic hinge that would have made it possible to reproduce about an 8-bit grayscale according to the conventional control.

In the single-panel projection apparatus described above, an example configuration attempting to obtain, for example, 13-bit grayscale is as follows:

LSB time=( 1/60)*(⅓)*(½¹³)=0.68 μsec

If a configuration is such that the light intensity obtained in one cycle for the optical comprisal is 38% of the intensity of the case controlling a mirror under a constant ON for the same cycle, the oscillation cycle T is as follows:

T=0.68/38%=1.8 μsec

In contrast, when an 8-bit grayscale is attempted to be obtained in the multi-panel projection apparatus described above, an example comprisal is as follows:

LSB time=( 1/60)*(⅓)*(½⁸)=21.7 μsec

If a configuration is such that the light intensity obtained in one cycle for the optical comprisal is 20% of the case controlling a mirror under a constant ON for the same cycle, the oscillation cycle T is as follows:

T=21.7/20%=108.5 μsec.

As described above, the present embodiment is configured to set the natural oscillation cycle of the oscillation system, which includes an elastic hinge, between about 1.8 μsec and 108.5 μsec; and to use three deflection state, i.e., a first deflection state, in which the light modulated by the mirror element is headed to the projection light path, a second deflection state, in which the light is headed to elsewhere other than the projection light path, and a third deflection state, in which the mirror oscillates between the first and second deflection states, thereby enabling the display of a high gray scale image without increasing the drive voltage of the mirror element.

As described above, the present embodiment is configured to make the electrode also function as stopper regulating the deflection angle of the mirror, thereby making it possible to improve a space usage efficiency, when the mirror element is miniaturized, and expand the area of the electrode.

<<Disclosure Content 2>>

The following is a description, in detail, of the preferred embodiment of the present invention by referring to the accompanying drawings.

FIG. 6 is a conceptual diagram showing the configuration of a projection apparatus according to a preferred embodiment of the present invention.

A projection apparatus 5010 according to the present embodiment comprises a single spatial light modulator (SLM) 5100, a control unit 5500, a Total Internal Reflection (TIR) prism 5300, a projection optical system 5400 and a light source optical system 5200 as exemplified in FIG. 6.

The projection apparatus 5010 is a so-called single-panel projection apparatus 5010 comprising a single spatial light modulator 5100.

The projection optical system 5400 is equipped with the spatial light modulator 5100 and TIR prism 5300 in the optical axis of the projection optical system 5400, and the light source optical system 5200 is equipped in such a manner that the optical axis thereof matches that of the projection optical system 5400.

The TIR prism 5300 fills the function of making an illumination light 5600, which is incoming from the light source optical system 5200 placed onto the side, enter the spatial light modulator 5100 at a prescribed inclination angle relative thereto as incident light 5601 and making a reflection light 5602 reflected by the spatial light modulator 5100 transmit so as to reach the projection optical system 5400.

The projection optical system 5400 projects the reflection light 5602 incoming by way of the spatial light modulator 5100 and TIR prism 5300 to a screen 5900 and such, as projection light 5603.

The light source optical system 5200 comprises a variable light source 5210 for generating the illumination light 5600, a condenser lens 5220 for focusing the illumination light 5600, a rod type condenser body 5230 and a condenser lens 5240.

The variable light source 5210, condenser lens 5220, rod type condenser body 5230 and condenser lens 5240 are sequentially placed in the aforementioned order in the optical axis of the illumination light 5600 emitted from the variable light source 5210 and incident to the side face of the TIR prism 5300.

The projection apparatus 5010 employs a single spatial light modulator 5100 for implementing a color display on the screen 5900 by means of a sequential color display method.

That is, the variable light source 5210, comprising a red laser light source 5211, a green laser light source 5212 and a blue laser light source 5213 (which are not shown in a drawing here) that allows independent controls for the light emission states, performs the operation of dividing one frame of display data into a plurality of sub-fields (i.e., three sub-fields, that is, red (R), green (G) and blue (B) in the present case) and making each of the red laser light source 5211, green laser light source 5212 and blue laser light source 5213 emit each respective light in time series at the time band corresponding to the sub-field of each color as described later. The light sources are laser light sources in the example, but the light sources may be semiconductor light sources such as LEDs.

FIG. 7 is a conceptual diagram showing the configuration of a projection apparatus according to another preferred embodiment of the present invention.

The projection apparatus 5020 is a so-called multiple-plate projection apparatus comprising a plurality of spatial light modulators 5100, which is the difference from the above described projection apparatus 5010. Further, the projection apparatus 5020 comprises a control unit 5502 in place of the control unit 5500.

The projection apparatus 5020 comprises a plurality of spatial light modulators 5100, and is equipped with a light separation/synthesis optical system 5310 between the projection optical system 5400 and each of the spatial light modulators 5100.

The light separation/synthesis optical system 5310 comprises a plurality of TIR prisms, i.e., a TIR prism 5311, a prism 5312, and a prism 5313.

The TIR prism 5311 has the function of leading the illumination light 5600 incident from the side of the optical axis of the projection optical system 5400 to the spatial light modulator 5100 as incident light 5601.

The TIR prism 5312 has the functions of separating red (R) light from an incident light 5601 incident by way of the TIR prism 5311 and making the red light incident to the red light-use spatial light modulators 5100, and the function of leading the reflection light 5602 of the red light to the TIR prism 5311.

Likewise, the prism 5313 has the functions of separating blue (B) and green (G) lights from the incident light 5601 incident by way of the TIR prism 5311 and making them incident to the blue color-use spatial light modulators 5100 and green color-use spatial light modulators 5100, and the function of leading the reflection light 5602 of the green light and blue light to the TIR prism 5311.

Therefore, the spatial light modulations of three colors of R, G and B are simultaneously performed at three spatial light modulators 5100, respectively, and the reflection light 5602 resulting the respective modulations are projected onto the screen 5900 as the projection light 5603 by way of the projection optical system 5400, and thus a color display is carried out.

Note that various modifications are conceivable for a light separation/synthesis optical system, in lieu of being limited to the light separation/synthesis optical system 5310.

FIG. 8A is a block diagram exemplifying the configuration of the control unit 5500 comprised in the above described single-panel projection apparatus 5010. The control unit 5500 comprises a frame memory 5520, an SLM controller 5530, a sequencer 5540, a light source control unit 5560 and a light source drive circuit 5570.

The sequencer 5540, constituted by a microprocessor and the like, controls the operation timing and the like of the entirety of the control unit 5500 and spatial light modulators 5100.

The frame memory 5520 retains the amount of, for example, one frame of input digital video data 5700 incoming from an external device (not shown in a drawing herein), which is connected to a video signal input unit 5510. The input digital video data 5700 is updated, moment by moment, every time the display of one frame is completed.

The SLM controller 5530 processes the input digital video data 5700 read from the frame memory 5520 as described later, separates the read data into a plurality of sub-fields 5701 through 5703, and outputs them to the spatial light modulators 5100 as binary data 5704 and non-binary data 5705, which are used for implementing an the ON/OFF control and oscillation control (which are described later) of a mirror 5112 of the spatial light modulator 5100.

The sequencer 5540 outputs a timing signal to the spatial light modulators 5100 synchronously with the generation of the binary data 5704 and non-binary data 5705 at the SLM controller 5530.

The video image analysis unit 5550 outputs a image analysis signal 5800 used for generating various light source pulse patterns (which are described later) on the basis of the input digital video data 5700 inputted from the video signal input unit 5510.

The light source control unit 5560 controls, by way of the light source drive circuit 5570, the operation of the variable light source 5210 emitting the illumination light 5600 by using a light source profile control signal, which is generated from the image analysis signal 5800 on the basis of the input of the image analysis signal 5800 obtained from the video image analysis unit 5550 by way of the sequencer 5540 and which generates light source pulse patterns 5801 through 5811 (which are described later).

The light source drive circuit 5570 performs the operation of driving the red laser light source 5211, green laser light source 5212 and blue laser light source 5213 of the variable light source 5210 to emit light, respectively, so as to generate the light source pulse patterns 5801 through 5811 (which are described later), which are input from the light source control unit 5560.

FIG. 8B is a block diagram exemplifying the configuration of the control unit of a multi-panel projection apparatus according to the present embodiment.

The control unit 5502 comprises a plurality of SLM controllers 5531, 5532 and 5533, which are used for controlling each of the plurality of spatial light modulators 5100 equipped for the respective colors R, G and B, and the comprisal of the controllers is the difference from the above described control unit 5500, otherwise similar.

That is, the SLM controller 5531, SLM controller 5532 and SLM controller 5533 corresponding to the respective color-use spatial light modulators 5100 are equipped on the same substrates as those of the respective spatial light modulators 5100. This configuration makes it possible to place the individual spatial light modulators 5100 and the respectively corresponding SLM controller 5531, SLM controller 5532 and SLM controller 5533 close to each other, thereby enabling a high speed data transfer rate.

Further, a system bus 5580 is equipped for commonly connecting the frame memory 5520, light source control unit 5560, sequencer 5540 and SLM controllers 5531 through 5533, in order to speed up and simplify the connection path of each connecting element.

FIG. 9 is a conceptual diagram exemplifying the configuration of the light source drive circuit 5570 (i.e., the light source drive circuits 5571, 5572 and 5573) according to the present embodiment.

The light source drive circuit exemplified in FIG. 9 comprises a plurality of constant current circuits 5570 a (i.e., I (R, G, B)₁ through I (R, G, B)_(n)) and a plurality of switching circuits 5570 b (i.e., switching circuits SW (R, G, B)₁ through SW (R, G, B)_(n)), which correspond to the respective constant current circuits 5570 a, in order to obtain the desired light intensities of emission P₁ through P_(n) for the light source optical system 5200 (i.e., the red laser light source 5211, green laser light source 5212 and blue laser light source 5213).

The switching circuit 5570 b carries out a switching in accordance with a desired emission profile of the light source optical system 5200 (i.e., the red laser light source 5211, green laser light source 5212 and blue laser light source 5213).

The setup values of the output current of the constant current circuits 5570 a (i.e., constant current circuits I (R, G, B)_(n)), when the gray scale of the emission intensity of the light source optical system 5200 is designated at N bits (where N≧n), are as follows:

I(R, G, B)₁ = I_(th) + LSB I(R, G, B)₂ = LSB + 1 I(R, G, B)₃ = LSB + 2 … … I(R, G, B)_(n) = MSB

Here, what is shown is an example of a gray scale display on the basis of an emission intensity; a similar gray scale display is achievable even if the emission period (i.e., an emission pulse width), emission interval (i.e., an emission cycle), and the like, are made to be variable.

The relationship between the emission intensity Pn of the variable light source and drive current for each color in this case is as follows. Note that “k” is an emission efficiency corresponding to the drive current:

P₁ = k * (I_(th) + I₁) P₂ = k * (I_(th) + I₁ + I₂) … … P_(n) = k * (I_(th) + I₁ + I₂ + … + I_(n − 1) + I_(n))

FIG. 10 is a chart showing the relationship between the applied current I and emission intensity P_(n) of the constant current circuit 5570 a of the light source drive circuit shown in the above described FIG. 9.

Note that the description for FIG. 9 has been provided for the case of changing the emission profiles of the variable light source for each sub-frame corresponding to each gray scale bit; if the display gray scale function of the spatial light modulator 5100 is used in parallel, the number of required levels of electrical current decreases, enabling the reduction in the numbers of constant current circuits 5570 a and switching circuits 5570 b and also making it possible to obtain the number of gray scales equal to, or higher than, the displayable gray scales of the spatial light modulator 5100.

Next is a description, in detail, of an example of the configuration of the spatial light modulator 5100 according to the present embodiment.

The spatial light modulator 5100 according to the present embodiment is a deflectable mirror device that arranges, in array a plurality of mirror elements.

FIG. 11 is a conceptual diagram exemplifying the layout of the internal configuration of the spatial light modulator 5100 according to the present embodiment.

FIG. 12 is a cross-sectional diagram of an individual pixel unit constituting the spatial light modulator 5100 according to the present embodiment; and FIG. 13 is a conceptual diagram exemplifying the configuration of individual pixel unit constituting the spatial light modulator 5100 according to the present embodiment.

As exemplified in FIG. 11, the spatial light modulator 5100 according to the present embodiment comprises a mirror element array 5110, column drivers 5120, ROW line decoders 5130 and an external interface unit 5140.

The external interface unit 5140 comprises a timing controller 5141 and a selector 5142. The timing controller 5141 controls the ROW line decoder 5130 on the basis of a timing signal from the SLM controller 5530. The selector 5142 supplies the column driver 5120 with digital signal incoming from the SLM controller 5530.

In the mirror element array 5110, a plurality of mirror elements are arrayed at the positions where individual bit lines 5121, which are vertically extended respectively from the column drivers 5120, crosses individual word lines 5131 which are horizontally extended respectively from the ROW decoders 5130.

As exemplified in FIG. 12 the individual mirror element 5111 comprises a mirror 5112 being freely tiltably supported on a substrate 5114 by way of a hinge 5113. The mirror 5112 is covered with a cover glass 5150 for protection.

An OFF electrode 5116 (and an OFF stopper 5116 a) and an ON electrode 5115 (and an ON stopper 5115 a) are placed by positioning them symmetrically across the hinge 5113 on the substrate 5114.

The OFF electrode 5116 attracts the mirror 5112 with a coulomb force by the application of a predetermined voltage and tilts the mirror 5112 to a position contacting with the OFF stopper 5116 a. This causes the incident light 5601 incident to the mirror 5112 to be reflected to the light path of an OFF position that is offset from the optical axis of the projection optical system 5400.

The ON electrode 5115 attracts the mirror 5112 with a coulomb force by the application of a predetermined voltage and tilts the mirror 5112 to a position contacting with the ON stopper 5115 a. This causes the incident light 5601 incident to the mirror 5112 to be reflected to the light path of an ON position matching the optical axis of the projection optical system 5400.

<<Disclosure Content 4>>

The following is a description, in detail, of the preferred embodiment of the present invention by referring to the accompanying drawings.

The following description provides various embodiments, with the configurations and operations of the projection apparatuses exemplified in the above described FIGS. 6 through 13 taken into consideration. Note that the same reference symbol is assigned to the same constituent component comprised in the above described promised configurations, and an overlapping description is not provided here.

Incidentally, a spatial light modulator 5100 comprising a mirror device used in a projection apparatus according to the present embodiment is configured to perform a linear gray scale display, unlike a conventional display apparatus such as CRT.

Therefore, as exemplified in FIG. 14, when a γ correction, such as an input data γ curve 7700 a, is applied to a piece of input digital video data 5700 at the transmission source (i.e., where the imaging is carried out) assuming a display in the CRT, a projection apparatus comprising a display device other than the CRT is required to restore the characteristic of a gray scale display to the original state (e.g., a conversion line 7700L for performing a linear conversion of a brightness signal in terms of an input data signal) by means of a correction such as a γ correction curve 7700 b and/or to perform a various γ corrections in accordance with the characteristics, and the like, of the projection apparatuses 5010, and 5020.

In such a case, a mathematical operation for the input digital video data 5700, as it is performed in a conventional display device, causes the circuit scale of the control unit 5500 to increase, leading to a higher production cost.

The present embodiment is accordingly configured such that the above described video image analysis unit 5550 changes the emission pattern of the illumination light 5600 emitted from a variable light source 5210 to the profile, as indicated by a γ correction light intensity variation 7800 a, so as to follow the above noted γ correction curve 7700 b, as exemplified in FIG. 15, and thereby a linear gray scale display as indicated by the conversion line 7700L is attained by negating the influence of the input data γ curve 7700 a performed at the transmission source without requiring a mathematical operation of the input digital video data 5700.

Note that this configuration makes it possible to not only restore the linearity by negating the influence of the input data γ curve 7700 a but also change, intentionally nonlinearly, the emission intensities of the variable light source 5210 within one frame as described in the following, thereby enabling various and highly precise gray scale display in excess of the original gray scale control capability of the spatial light modulator 5100.

As an example, a video image output (i.e., the input digital video data 5700) contains various scenes such as a dark scene, a bright scene, a generally bluish scene and a generally reddish scene such as the evening glow. The projection apparatus according to the present embodiment is configured to control the gray scale of the emission output of the variable light source 5210 most optimally in dependence on the respective scene (with actual control carried out in units of frame), thereby making it possible to attain prettier video images.

Incidentally, when a γ correction of the input digital video data 5700 (i.e., the input data γ curve 7700 a) is implemented by means of a temporal change in emission intensities of the variable light source 5210 as described above, a precise emission control of the variable light source 5210 is difficult if an ON/OFF control of the mirror 5112 through a pulse width modulation (PWM) using binary data 7704 included in the input digital video data 5700 is carried out.

Accordingly, the SLM controller 5530 according to the present embodiment is configured to carry out an ON/OFF control of the mirror 5112 using non-binary data 7705 obtained by converting binary, data 7704 as exemplified in FIGS. 16, 17, 18 and 19.

That is, FIG. 16 exemplifies the case of generating non-binary data 7705, which is a bit string having an equal weighting for each digit, from the binary data 7704 that is constituted by, for example, 8-bit “10101010”, and a control is carried out for turning ON the mirror 5112 only for a period in which the bit string continues.

Note that FIG. 16 exemplifies the case of converting the non-binary data 7705 so that the bit string is packed forward within the display period of one frame, and controlling the mirror 5112 so as to be turned ON for a predetermined period in accordance with the bit string number from the beginning of a frame display period.

Likewise, FIG. 17 exemplifies the case of converting 8-bit “01011010” binary data 7704 into non-binary data 7705 that is a forward-packed bit string.

Further, FIG. 18 exemplifies the case of converting the binary data 7704 exemplified in the above described FIG. 16 into a bit string of non-binary data 7705 with the digits packed backward. In this case, the mirror 5112 is controlled so as to be turned ON only in the period of time corresponding to the bit string number starting from the midst of a frame display period until the end thereof.

Likewise, FIG. 19 exemplifies the case of converting the binary data 7704 exemplified in the above described FIG. 17 into a bit string of non-binary data 7705 with the digits packed backward and controlling the ON/OFF of the mirror 5112.

When the ON/OFF is controlled by the non-binary data 7705 as described above, the ON period of the mirror 5112 becomes continuous, and therefore a control of the emission intensity of the variable light source 5210 in synchronous with the aforementioned ON period becomes easy.

FIG. 20 exemplifies the case of the brightness input of 8-bit non-binary data 7705 into, for example, four steps, i.e., 64, 128, 192 and 255, as shown in the upper rows of FIG. 20, and obtaining a γ correction curve 7700 c as shown in the lower row of the drawing through a four-step control of the output intensity of the variable light source 5210 in response to the each of the aforementioned levels, as indicated by a light source pulse pattern 7801 shown in the middle row of the drawing.

For simplicity, FIG. 20 exemplifies the case of performing a control in four steps, a further minute grouping of the non-binary data 7705 makes it possible to obtain a smoother curve than the γ correction curve 7700 c.

Note that the example of FIG. 20 shows that the correction amount of the γ correction curve 7700 c is in shortage on the brighter side when compared with the conversion line 7700L.

Accordingly, the emission pattern of the variable light source 5210 may be controlled so as to move a γ correction curve 7700 d close to the above described conversion line 7700L as indicated in the bottom part of FIG. 21 by increasing, from the emission intensity H0 to the emission intensity H1, the emission intensity of the light source pulse toward the tail end of the display period of one frame as indicated by a light source pulse pattern 7802, as exemplified in FIG. 21.

The above described FIGS. 20 and 21 exemplify the case of performing a γ correction by changing the emission intensity while maintaining the variable light source 5210 continuously emitting light as indicated by the light source pulse patterns 7801 and 7802; the control may be performed by means of an intermittent pulse emission.

FIG. 22 exemplifies a control by means of the aforementioned intermittent pulse emission. A light source pulse pattern 7803 exemplified in FIG. 22 causes to generate emission pulses having an emission pulse width tp intermittently in intervals of emission pulse intervals ti and increases the number of emission pulses per unit time by gradually decreasing the emission pulse interval ti between the beginning and end of the display period of one frame, thereby attaining an effect similar to that of the above described continuous light source pulse patterns 7801 and 7802.

Further, the light source pulse pattern 7804 exemplifies the case of gradually increasing the emission pulse width tp between the beginning and end of the display period of one frame.

Further, the light source pulse pattern 7805 exemplifies the case of gradually decreasing the emission pulse intervals ti and also gradually increasing the emission pulse width tp between the beginning and end of the display period of one frame.

Further, the light source pulse pattern 7806 exemplifies the case of gradually increasing both the emission pulse width tp and emission intensity H2 between the beginning and end of the display period of one frame.

FIGS. 23A and 23B exemplify the case of attaining a γ correction curve 7700 e performing γ correction for increasing a correction effect on the lower brightness side by means of a light source pulse pattern 7807.

That is, the light source pulse pattern 7807 shown in FIG. 23A controls the emission pattern of the variable light source 5210 so as to cause the generation of a plurality of emission pulses having a constant emission pulse width tp densely (that is, the emission pulse interval is small) on the start side (i.e., the lower density side) of the display period of one frame, and to gradually decrease the number of pulses (that is, the emission pulse interval ti gradually increases) toward the end of the display period.

This control makes it possible to attain a γ correction curve 7700 e which is convex-shaped toward the top-left of the conversion line 7700L and which accordingly provides a large correction effect, i.e., increasing brightness, on the lower brightness side, as exemplified in FIG. 23B.

FIGS. 24A and 24B exemplify the case of a γ correction considering the visual characteristic of human being by a control of the variable light source 5210 with a light source pulse pattern 7808.

That is, the human eye is known to possess high sensitivity in the middle of low brightness and high brightness. Accordingly, a γ correction is performed by controlling the variable light source 5210 with the light source pulse pattern 7808 that makes emission pulses having the same emission pulse width tp be dense (i.e., making the emission pulse interval ti small) at the center of the display period of one frame and gradually decreases the density of the emission pulse toward either side, as exemplified in FIG. 24A.

This control attains a γ correction using a γ correction curve 7700 f that is smaller than the conversion line 7700L on the lower brightness side and larger than that on the higher brightness side, thereby making it possible to obtain a modulated and clear projection image, i.e., darker on low brightness side and brighter on high brightness side, as shown in FIG. 24B.

Also, the gamma correction by means of the modulation in the light source as implemented in the present embodiment performed after performing the conventional gamma correction of performing the above mathematical operation by using a gamma correction circuit makes it possible to perform gamma correction that is more appropriate to the mirror device than the conventional correction.

Next is an example of expanding the number of display gray scales by performing a modulation control of the accumulated maximum light intensity in the display period of one frame corresponding to the variable light source 5210 of each color so as to obtain a desired output light intensity corresponding to the pixel data indicating the maximum brightness.

The maximum gray scale output provided by a spatial light modulator 5100 comprising a mirror device is determined by the operation speed of the ON/OFF control of a mirror (more specifically, however, it is affected by other factors such as single-panel comprisal versus multi-panel comprisal and the number of sub-frames to be divided into).

For example, if an 8-bit gray scale output is the maximum according to the operation speed of the mirror 5112, a 256-step gray scale, i.e., “0” through “255”, can be output. If a single color gradation is displayed, the gradation is 256 steps; the gradation recognition capability of human being exceeds such steps (it is believed to require 12-bit) that is not viewed as a smooth gradation, but as stepwise borders.

In practice, however, there are few scenes to output the entire gray scales of “0” through “255”, and instead, there are cases of outputting only outputting “0” through “128” such as in a movie, or even only darker gray scale parts. The visual recognition capability of human being is particularly better with the difference in dark areas than that in bright areas, and therefore a person tends to recognize a minute difference in brightness of a dark scene as a border line.

The present embodiment is accordingly configured to perform a modulation control of an accumulated maximum light intensity in the display period of one frame corresponding to the variable light source 5210 of each color so that a desired output light intensity corresponding to the maximum brightness pixel data is obtained. This control makes it possible to express the brightness from the brightest part (i.e., the pixel) to the total darkness (i.e., “0” brightness) of a scene (i.e., frame) by the maximum gray scale output of a mirror, thereby smoothing and beautifying video image especially in a dark scene.

That is, the upper part of FIG. 25 shows the case of making the variable light sources 5210 (i.e., the red laser light source 5211, green laser light source 5212 and blue laser light source 5213) emit light continuously at a constant emission intensity H10 in the gray scale display control of the respective colors in, for example, the multi-panel projection apparatus 5020 and turning ON/OFF the mirrors 5112 in accordance with the mirror control profile 7706 (for red), mirror control profile 7707 (for green) and mirror control profile 7708 (for blue) by means of the PWM, and thereby a gray scale display is attained.

When performing a gray scale control by means of the ON/OFF control of the mirror 5112, there is a case in which a smooth gray scale cannot be expressed because the expression depends on the gray scale expression of the data width of the input digital video data 5700. Further, the light sources of the respective colors become a constant emission state independent of the gray scale change of the respective colors, wasting the emission energy.

In contrast, the present embodiment is configured to maintain the mirror 5112 of a pixel, which indicates the maximum brightness, continuously in the ON state (in accordance with the mirror control profiles 7706 a, 7707 a and 7708 a) and set the variable light sources 5210 (i.e., the red laser light source 5211, green laser light source 5212 and blue laser light source 5213), which output the illumination light 5600, at emission intensities H11 (for red), H12 (for green) and H13 (for blue), which correspond to the gray scale data indicating the maximum brightness, in the gray scale control of each color as exemplified on the lower side of FIG. 25, and thereby the gray scale can be expressed by the maximum gray scale output (that is, a continuous ON state in one frame period) of the mirror 5112, smoothing out and beautifying the video image especially in a dark scene.

Further, the brightness of the respective colors R, G and B are attained by the increase/decrease in the intensity of the illumination light 5600 output from the corresponding variable light sources 5210 (i.e., the red laser light source 5211, green laser light source 5212 and blue laser light source 5213), saving energy and reducing an unnecessary light component, and therefore the contrast is improved in the video image.

Note that, while the above described FIG. 25 exemplifies the case of controlling the variable light sources 5210 to be continuously turned on at the emission intensities H11, H12 and H13, respectively, in the gray scale control of the respective colors, the variable light sources 5210 may be controlled with an intermittent emission pulse, as shown in FIG. 26.

That is, in FIG. 26, the mirror 5112 of a pixel indicating the maximum brightness is maintained at a continuous ON in one frame period, as represented by the mirror control profiles 7706 a, 7707 a and 7708 a in the display control of the respective colors, whereas the variable light sources 5210 are configured to pulse-emit in accordance with the emission pulse width tp and emission pulse interval ti, as represented by light source pulse patterns 7809 b (for red), 7810 b (for green) and 7811 b (for blue).

In this event, the number of emission pulses is controlled so that the total intensity of the emission pulse is equivalent to the gray scale data of a pixel indicating the maximum brightness.

Also in this case, the gray scale can be expressed by the maximum gray scale output (that is, a continuous ON state in one frame period) of the mirror 5112, smoothing out and beautifying the video image especially in a dark scene.

Further, the brightness of the respective colors R, G and B are attained by the increase/decrease in the intensity of the corresponding variable light sources 5210 (i.e., the red laser light source 5211, green laser light source 5212 and blue laser light source 5213), saving energy and reducing an unnecessary light component, and thereby the contrast in the video image is improved.

FIG. 27 exemplifies the case of performing a gray scale control when the gray scale control exemplified in the above described FIGS. 25 and 26 is applied to a single-panel projection apparatus 5010.

In this case, the display period of one frame is divided into a plurality of subfields 5701, 5702 and 5703 corresponding to the respective colors R, G, and B, and a color display is attained by a color sequence method.

Meanwhile, in the case of the conventional method, the ON/OFF control for the mirror 5112 is performed, by means of a PWM, in accordance with the mirror control profiles 7706 (for red), 7707 (for green) and 7708 (for blue) in the respective subfields, and the variable light sources 5210 perform a continuous emission at a constant intensity level in accordance with the light source pulse patterns 7809, 7810 and 7811, thereby performing a gray scale control, as shown on the upper part of FIG. 27. In this case, a gray scale expression depends on that of the data width of input digital video data 5700 and therefore there is a possibility that a smooth gray scale expression cannot be attained as described above.

In contrast, as shown on the lower part of FIG. 27, the present embodiment is configured to perform a control so that the mirror 5112 of a pixel indicating the maximum brightness is controlled to the ON state in the entire display period of one frame (i.e., the entire subfields) in accordance with the mirror control profiles 7706 a, 7707 a and 7708 a, and so that the intensity of the variable light sources 5210 are set at intensity equivalent to the gray scale data of a pixel indicating the maximum brightness (i.e., the emission intensities H11 (for red), H12 (for green) and H13 (for blue)), and thereby the gray scale can be expressed by the maximum gray scale output (that is, a continuous ON state during the period of one frame) of the mirror 5112, thus smoothing out and beautifying the video image especially in a dark scene.

FIG. 28 shows the case of attaining an intensity equivalent to the above described emission intensities H11, H12 and H13 by adjusting the emission pulse width tp and emission pulse interval ti of the emission pulse by means of an intermittent pulse emission of the variable light sources 5210 in the respective subfields of red, green and blue. Also in this case, an effect similar to the case of the above described FIG. 27 is obtained.

FIG. 29 shows a capability of a grayscale control with a wide dynamic range than the case of making the emission intensity of the variable light source 5210 by combining the ON/OFF control of the mirror 5112 and the emission intensity control of the variable light source 5210 in the above described various control examples.

That is, if the emission intensity level of the variable light source 5210 is constant at the emission intensity H20, with a gray scale expression in 256 steps, that is, “0” through “255”, in accordance with, for example, input digital video data 5700 only being possible in the range between the full ON and full OFF of the mirror 5112 and a pixel indicating the maximum brightness being a half light intensity, i.e., “0” through “127”; then a 128-step gray scale, i.e., “0” through “127”, can only be expressed, as shown on the upper part of FIG. 29.

In contrast, when the emission intensity of the variable light source 5210 is controlled, the maintaining of the emission intensity H21 of the variable light source 5210 at one half of the emission intensity H20, as in the present embodiment, makes it possible to attain a 256-step grayscale expression, i.e., “0” through “255”, in the range between the full ON and full OFF of the mirror 5112, as shown on the lower part of FIG. 29.

That is, the width of the grayscale expression can be represented more minutely in excess of the designation range of the input digital video data 5700, thus improving the image quality.

Next is a description of an example of countermeasures to a color break. In the case of a multi-panel projection apparatus comprising a plurality of spatial light modulators 5100, as in the above described projection apparatus 5020, there is a concern that, if the output time for each color is different, a state in which only a certain color is output is created, resulting in the occurrence of a color break, in which the individual colors R, G and B are singularly visible to some people.

Accordingly, the present embodiment is configured to equip the SLM controller 5530 controlling the spatial light modulators 5100 with the function of controlling the mirror 5112 of the spatial light modulators 5100 to either condition of the changeover between the ON state and OFF state and the intermediate output state, in which the mirror5112 oscillates between the ON and OFF states.

Further, if the brightness output value to be modulated is no smaller than the brightness output of a case in which the intermediate output state is continued in the entire display period of one frame for each color, the modulation is performed in the combination between the ON state and intermediate output state of the mirror 5112 for the display period of one frame for each color.

FIG. 30 exemplifies the control for such a countermeasure to a color break. A mirror control profile 7711 drawn at the center of FIG. 30 indicates the case of a brightness output carrying out a mirror oscillation control 7710 b in the entire display period of one frame for each color.

Further, the present embodiment is configured to continue to output light in the entire display period of one frame by the combination between a mirror ON/OFF control 7710 a and the mirror oscillation control 7710 b as indicated by the mirror control profile 7710 on the top side of FIG. 30 in the case in which the brightness output is no less than the mirror control profile 7711.

In contrast, in the case in which the brightness output is no more than the mirror control profile 7711, a required brightness output is attained by controlling a continuation time period of the mirror oscillation control 7710 b during the display period of one frame as shown on the lower side of FIG. 30.

The control exemplified in FIG. 30 makes it easy to align the output time for each color, thereby reducing a possibility of the occurrence of a color break in the projection apparatus 5020 comprising a plurality of spatial light modulators 5100.

Note that, if a grayscale control is carried out by controlling the intensity by setting the emission pulse width tp and emission pulse interval ti of the variable light source 5210, as in the above described FIGS. 26, 28, et cetera, the light source control unit 5560 is also capable of performing a control so as to increase the maximum brightness of the variable light source 5210 by selectively narrowing the emission pulse interval ti within a specific unit time during a one-frame period for a frame of a specific condition of the input digital video data 5700 when the output of the illumination light 5600 is modulated by varying the emission pulse interval ti (i.e., the emission interval cycle) of the pulse emission of the variable light source 5210.

As such, the taking advantage of so-called peak brightness of the variable light source 5210 widens the dynamic range of a video image output, thereby making it possible to obtain a further powerful video image.

That is, the configuration is for increasing the peak brightness of the variable light source 5210 by putting it in over-drive only when displaying a scene (i.e., a frame) in which, for example, only a small part of a screen is very bright, or the like scene, as described above because a continuous setup of the maximum brightness will adversely affects the life, et cetera, of the variable light source 5210.

Note that the present invention can be modified in various manners possible within the scope of the present invention, in lieu of being limited to the configurations exemplified in the above described preferred embodiments. 

1. A projection apparatus, comprising: a light source; a light source control unit for controlling output of the light source; at least one spatial light modulator for modulating illumination light from the light source by a plurality of pixel elements; and an optical system for projecting, to a screen, the illumination light deflected by the spatial light modulator, wherein: the light source control unit modulates output of the illumination light from the light source during a modulation period of the spatial light modulator, and non-linearly controls gray scale of a projected image projected to the screen.
 2. The projection apparatus according to claim 1, wherein: the light source control unit modulates output of the illumination light by making an intensity of the illumination light variable.
 3. The projection apparatus according to claim 1, wherein: the light source control unit modulates output of the illumination light by making an emission interval cycle of pulse emission of the light source variable.
 4. The projection apparatus according to claim 1, wherein: the light source control unit modulates output of the illumination light by making an emission interval cycle of pulse emission of the light source constant and by making an emission pulse time variable.
 5. The projection apparatus according to claim 1, wherein: the light source control unit modulates output of the illumination light by making an emission interval cycle and an emission pulse time of pulse emission of the light source variable.
 6. The projection apparatus according to claim 1, wherein: the light source control unit modulates output of the illumination light γ making at least one of an emission interval cycle, an emission pulse time, and an emission pulse intensity of pulse emission of the light source variable.
 7. The projection apparatus according to claim 1, wherein: the light source control unit modulates output of the illumination light by input image data.
 8. The projection apparatus according to claim 1, wherein: the light source control unit increases maximum brightness of the light source by making an emission interval cycle of the pulse emission variable within a particular time of one frame when output of the illumination light is modulated by making an emission interval cycle of pulse emission of the light source variable.
 9. The projection apparatus according to claim 1, wherein: the spatial light modulator comprises a micromirror device in which a plurality of mirror elements for deflecting light from the light source are arranged.
 10. The projection apparatus according to claim 1, wherein: the light source is a light emitting diode (LED) or a laser device.
 11. A projection apparatus, comprising: at least one light source provided for each of colors of illumination light; a light source control unit for controlling output of the light source; at least one spatial light modulator for modulating the illumination light from the light source by a plurality of pixel elements; and an optical system for projecting, to a screen, the illumination light modulated by the spatial light modulator, wherein: the light source control unit modulates a projected image by changing an emission energy of cyclic pulse emission for each color of the illumination light emitted from the light source.
 12. The projection apparatus according to claim 11, wherein: the light source control unit changes emission pulse width of the cyclic pulse emission for each color of the illumination light emitted from the light source.
 13. The projection apparatus according to claim 11, wherein: the light source control unit changes an emission pulse cycle of the cyclic pulse emission for each color of the illumination light emitted from the light source.
 14. The projection apparatus according to claim 11, wherein: the light source control unit changes an emission pulse intensity of the cyclic pulse emission for each color of the illumination light emitted from the light source.
 15. The projection apparatus according to claim 11, wherein: the light source control unit changes an emission interval cycle and emission pulse width of the cyclic pulse emission for each color of the illumination light emitted from the light source.
 16. The projection apparatus according to claim 11, wherein: the light source control unit changes an emission interval cycle and an emission pulse intensity of the cyclic pulse emission for each color of the illumination light emitted from the light source.
 17. The projection apparatus according to claim 11, wherein: the light source control unit changes emission pulse width and an emission pulse intensity of the cyclic pulse emission for each color of the illumination light emitted from the light source.
 18. The projection apparatus according to claim 11, wherein: the spatial light modulator comprises a micromirror device in which a plurality of mirror elements for deflecting light from the light source are arranged.
 19. The projection apparatus according to claim 11, wherein: the light source is a light emitting diode (LED) or a laser device.
 20. The projection apparatus according to claim 11, wherein: the light source control unit demodulates output of the illumination light by input image data.
 21. A projection apparatus, comprising: at least one light source provided for each of colors of illumination light; a light source control unit for controlling output of the light source; at least one micromirror device in which a plurality of mirror elements for deflecting the illumination light from the light source are arranged; a micromirror device control unit for controlling the micromirror device; and a projection optical system for projecting, to a screen, the deflected illumination light from the micromirror device, wherein: the light source control unit performs a modulation control of an accumulated maximum light intensity in a display period of one frame corresponding to the light source of each color of the illumination light.
 22. The projection apparatus according to claim 21, wherein: the micromirror device control unit causes the mirror element corresponding to pixel data of maximum brightness in the frame data for each color to be in a state of continuously leading the illumination light to the projection optical system during a display term of the one frame; and the light source control unit performs a modulation control so that a desired output light intensity corresponding to the pixel data of the maximum brightness is obtained.
 23. The projection apparatus according to claim 21, wherein: the light source is a light emitting diode (LED) or a laser device. 